It was a new, different, "softer" state/experience, chemical in nature; everyone likes it. We have chemicals in our body affecting our experience all the time; think of orgasm; "you" didn't do that. Think of how you feel when you first lay down in bed after a hard day of work or play (look at a child who comes in from chasing fireflies on a summer evening and wears him/herself out, look at a puppy); babies feel the same way suckling, pooping, etc. It is a good feeling all on its own, not related to whether or not you are a child or not, know how to define "stress" properly. Growth is stressful; think about all the new things you were confronted with as a child, something simple like your first day of school, never mind your first test